The human brain contains an estimated 100 billion nerve cells (neurons). Chemical and electrical activity allows these neurons to perform their tasks and to communicate with one another. This elaborate communication system controls vital body functions and enables us to think, see, move, talk, remember, and experience emotions.

There are four different memory systems of the brain -- episodic, semantic, procedural, and working.

Memory Systems of the Brain

1. Episodic Memory

The temporal lobe, which contains the hippocampus, and the prefrontal cortex are important to episodic memory, which enables us to learn new information and remember recent events. The hippocampus is one of the first brain structures damaged in Alzheimer's disease and accounts for one hallmark of early Alzheimer's:

difficulty remembering recent events, without any trouble remembering events from long ago.

2. Semantic Memory

Semantic memory governs general knowledge and facts, including the ability to recognize, name, and categorize objects. This system also involves the temporal lobes and, researchers suspect, multiple areas within the cortex. People with Alzheimer's disease may be unable to name a common object or to list objects in a category.

3. Procedural Memory

The cerebellum is one of the structures involved in procedural memory. Procedural memory is what enables people to learn skills that will then become automatic (unconscious), such as typing or skiing. This memory system typically is not damaged in Alzheimer's disease or is one of the last cognitive domains to deteriorate.

4. Working Memory

Working memory involves primarily the prefrontal cortex. This memory system governs attention, concentration, and the short-term retention of needed information, such as a street address or phone number. Problems with working memory can impair a person's ability to pay attention or to accomplish multi-step tasks. Numerous cognitive disorders, such as Alzheimer's, Parkinson's, and Huntington's disease as well as dementia with Lewy bodies, can affect working memory.

In a nutshell, persons living with Alzheimer's or dementia cannot remember to remember. As a result, they can no longer either recall or use new memories in the future.

Nevertheless, persons living with dementia continue to surprise us with their stories and memories of the past.

This is why I often referred to my mother as being deeply forgetful. My mother proved to me over and over that the deeply forgetful are in fact capable of living in the present - the right now.

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